Many radio-frequency (RF) communication antennas are planar antennas designed to be integrated with RF transmitting and receiving circuitries. A multi-layer planar antenna, which can be fabricated using the standard printed-circuit board (PCB) fabrication process, for example, may include various layers such as antenna layers (e.g., radiating layers), feed circuitry, and beam-forming portions. Planar antennas can take a variety of forms such as spiral, sinuous, and log periodic and are generally characterized by operational parameters such as gain, bandwidth, and voltage standing-wave ratio (VSWR) that are among the most important characteristics of RF antennas. The VSWR is the ratio of the amplitude of a partial standing wave at a maximum to an amplitude of the standing wave at a minimum. The antenna bandwidth can be defined as a contiguous band of frequencies in which the VSWR is below 2:1.
In order to minimize losses due to mismatch of the antenna layers to the feed circuitry, an impedance of the antenna layer has to be matched with the impedance of the feed circuitry. The matching of the antenna layer to the feed circuitry can affect the bandwidth, the VSWR, and the gain of the planar antenna. Therefore, for a wideband planar antenna, this impedance matching can have a profound effect on the antenna characteristics.